In supporting engines suspended on motor vehicles in a vibration-isolating manner, the number of revolutions per minute of the engines themselves varies over a wide range and consequently, vibration-absorbing mounts that are capable of fulfilling the two requirements are indispensable: for one thing, the damping coefficient must be large during high-amplitude oscillations, low-frequency oscillations occurring at low speed and for the other thing, vibration insulating ability is high against high frequency oscillations occurring at high speed. However, noises due to low frequency oscillations and noises due to high frequency oscillations are contrary to each other in characteristics, hence it is very difficult to solve both at the same time.
There have been heretofore provided rubber vibration insulating devices of a type in which a damper material such as rubber is used for a sealed annular elastic body and a damping liquid such as a non-freezing liquid is enclosed within the sealed annular body whereby a damper effect through an orifice is imparted. Some of them now find commercial acceptance.
However, existing devices of this type are constructed so that a partition wall provided in a damper liquid chamber formed by one mounting bracket and a diaphragm having an orifice in the lower part thereof has generally a high rigidity and is secured to the other mounting bracket. Hence, these have serious drawbacks in that dynamic spring rate in the high frequency oscillation region becomes large and the liquid pressure of the damper liquid chamber becomes high, which causes muffled sounds to be generated that impair quietness of the vehicle room. Here, if a partition wall having the function characteristic of absorbing small amplitude oscillations in the high frequency vibration region is used instead, then such function characteristics of it in the medium and low frequency regions will be poor.